Air Wall

Air Wall is a conjectural label, since the ability goes unnamed in the film itself. It is an Emitter power of short range belonging to Nine, who stole it from a Hero whose identity is never given, and it appears in My Hero Academia: Heroes: Rising.

Defense comes first with this one. Compressed air is shaped into shields and held between the wielder and whatever is coming at him.

Circular barriers form off the hands. They hold up under serious force, Izuku's Delaware Smash Air Force included, and can be stacked one behind another when more stopping power is called for. The user can also close them into a dome, covering every approach at once rather than a single line. A drug that empowered his Quirk let Nine put up one large rectangular barrier instead.

Offense comes out of the same material. A shield can be shoved forward to hurl people away, and the wielder can fire bursts of pressurized air strong enough to knock a target down and leave them stunned.

Two limits apply. The walls are tough but never indestructible, and their strength tracks how focused and healthy Nine is: at full power they hold, while his deteriorating condition left them shattering on the first impact. They also form only where he raises his hand, so a nimble enough opponent can work around that arc and hit the parts of him nothing is guarding.

Nine is the only wielder shown, and the ability sits among the several powers he assembled over the course of the film. The Hero he took it from is never identified.

Air Cannon, held by All For One and Tomura Shigaraki, runs on the same principle of weaponized compressed air, and the anime's later renderings of that Quirk came to look much like this one.